Linux operation and maintenance of the road network basic Learning 1.3

Network Fundamentals 1.3

Data Link Layer parsing:

Data Link Layer:

is located between the physical layer and the network layer;

Features of the data link layer:

--Establishment, maintenance, demolition of data link

--frame wrapping, frame transfer, frame synchronization

--Error recovery of frames

--Flow control

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Ethernet:

What is Ethernet:

--we usually use Ethernet;

--Ethernet works at the data link layer;

Ethernet MAC Address:
--The Ethernet address is used to identify a device or a group of devices on an Ethernet network;

802.3 Ethernet frame format;

Two sub-layers of the data link layer:

Media access Control sub-layer (MAC):

---the upper-layer data is encapsulated into frames for sending;

---Implement and maintain the media access control protocol;

---bit error detection;

addressing of--MAC addresses;

Logical Link Control sub-layer (LLC):

---to establish and release the logical connection of the data link layer;

---provide interfaces with the upper layer;

---to add a serial number to the frame;

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Ethernet Switch

What is a switch:
Switch is the main device used to connect LAN;

--The switch is capable of transmitting data intelligently according to the target Viao address in the Ethernet frame, so the switch works at the data link layer;

--The switch divides the conflict domain, realizes the whole double public communication;

How the Switch works:

1. Initial state
   

2. MAC Address Learning

3. Broadcast Unknown data frame

4. Response from the Receiving party

5. Switch implements single wave communication

Learn:

The--mac Address table is a broadcast that the switch forms by learning the source MAC address of the data frame received;

Broadcasting:

---If the destination address is not in the MAC address table, the switch broadcasts the data frame to all other ports in the port other than the port that received the data frame.

Forward:

---switch forwards data frames based on MAC Address Table single wave

Update:

--The Switch MAC Address table has an aging time of 300 seconds

---The switch learns the MAC address to the new port if it finds that the port of a frame differs from the one on which the source MAC address of the MAC Address table is located.

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Simplex, half duplex, full duplex:

Simplex: Only one channel, the transmission direction can only be unidirectional;

Half Duplex: Only one channel, at the same time, only one-way transmission;

Full duplex: Dual channel, simultaneously can have two-way data transmission;

Conflict and conflict domains:

-If there is too much conflict, the transmission efficiency will be reduced;

--in order to improve efficiency, divide the conflict domain;

Split Conflict Fields:

Switch backplane switching matrix structure;

--Each port of the switch accesses another port, there is a dedicated line, no conflict;

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Broadcast domain:

Broadcast domain refers to the collection of nodes that receive the same broadcast message.

The switch splits the conflict domain, but does not split the broadcast domain, that is, all the ports of the switch belong to the same broadcast domain;

Switch internal switching mode:

Store and forward:

---is the most widely used method in the field of computer network;

---error detection of packets entering the switch;

---support the conversion between ports at different speeds;

--large delay in data processing;

Fast forwarding:

---Delay is very small, exchange very fast;

---can not provide error detection capability;

---because there is no cache, can not be a port with different rates of input/output port directly connected, and easy to drop packets;

Segmented filtering:

---Checks if the packet is 64 bytes long, if it is less than 64 bytes, the packet is discarded, and if it is greater than 64 bytes, the packet is sent;

---does not provide data validation, it has to data processing faster than the storage and forwarding method, but faster than through-pass;

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Linux operation and maintenance of the road network basic Learning 1.3